Various known magnetic structures and techniques for designing such structures are disclosed, for example, in the technical reports "Generation of a Uniform Field in a Yokeless Permanent Magnet for NMR Clinical Applications", M. G. Abele and H. Rusinek, TR-19, NYU School of Medicine, New York, 1988 and "Optimum Designe of Two-Dimensionals Permanent Magnets", M. G. Abele, TR-21, NYU School of Medicine, New York, 1989, as well as in U.S. Patent applications Ser. Nos. 424,162, M. G. Abele, filed Oct. 19, 1989 (Case NYU127A), and 909,143, Abele et al, filed Jul. 6, 1992 (Case NYU130) and U.S. Pat. Nos. 5,107,239, Abele and 5,162,771, Abele. The contents of each of the above reports, patent applications and patents is incorporated herein by reference.
In a traditional design for a magnetic structure, the functions of generating and confining the field are assigned to separate components of a magnetic circuit. Such design starts with the specification of an assigned field within a given region of interest and the function of shaping the field is assigned to the ferromagnetic pole pieces. The region of interest in the structure is contained within the gap or cavity between the pole pieces whose shape is usually the most important part of the overall magnet design.